Manufacture of electrical conductors



Oct; 20, 1942. H. F. FRUTH MANUFACTURE OF ELECTRICAL CONDUCTORS ENAMELC014 TED Filed March 5, 1941 ENAMEL COMPOUND I'ENAMEL caupowvo 7 5 W W mWm A Mr i v Patented Oct. 20, 1942 UNITED STATES PATENT I OFFICEMANUFACTURE OF ELECTRICAL CONDUCTORS Hal r. Fruth, Ellnhurst, n1.,assignor to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York Application March 5, 1941, Serial No. 381,830 r6 Claims. (Cl. 117-128) other surface irregularities which extend fromthe wire surface into the coating and in some cases project through thecoating. When this wire is incorporated in electrical apparatus, such ascable or coils, where the wire turns are positioned closely together,these defective portions of the insulation may reduce the efficiency andthe service life of the apparatus.

An object of the presentinvention is the provision of improved,economical and efficient methods for applying a continuous and uniformFor example, wire may contain ridges, slivers and coating of enamelinsulation on electrical con- I ductors.

In accordance with one embodiment of the invention, a coating ofthermosetting insulating enamel is applied on a wire and the coated wireis then baked until the enamel becomes tough but not brittle. The wirewith the tough enamel coating is then drawn through a mass of hard andsubstantially spherical particles, such as shot or sand, to impact anddeform any ridges or other projections extending from the wire surfaceinto or through the enamel, after which a second coating of enamel isapplied on the wire and the wire is then baked to fully harden both ofthe coating layers.

The invention may be more clearly understood from the following detaileddescription taken in conjunction with the appended drawing, in whichFig. 1 is a side elevation of a wire coating apparatus suitable forpracticing one embodiment of the invention; I v

Fig. 2 is a front elevation of the wire coating apparatus shown in Fig.1, and i Fig. 3 is an enlarged view of a portion of the apparatus shownin Figs. 1 and 2.

In the wire coating art the term enamel is used broadly to define acomposition which is applied to the wire in liquid form and which iselectrically insulating coating on the wire. Three general types ofenamel are used, including the lacquer, varnish, and'combination types.The lacquer type is thermoplastic, usually having a cellulose nitrate orcellulose acetate base, and forms a solid film directly upon evaporationof the solvent. The varnish typeenamels are thermosetting and areProbably used most widely. They generally contain an oil, resin, drier,and solvent. The oil may be linseed or castor oil, and the resin may benatural, such as copal,

'kauri, etc., or it may be synthetic such as Bakelite, glyptal,cumarone, etc. The driers are usually soaps of such metals as lead,cobalt or manganese and any suitable solvent. .The drier contributeslittle if anything to the finished product but is necessary to reducethe consistency or yiscosity of the enamel to a usable state, may beused. On evaporation of the solvent, these varnish type enamels formliquid films which are solidified by baking. The third type, or thecombination type enamels, such as shellac base materials, form a solidfilm on evaporation of the solvent but baking at an increased temprature is necessary to provide the final film characteristics. ,JIhisinvention can be employed with any of the above enamel types but isespecially adapted to the varnish enamels and the following detaileddescription is directed to that class of material.

The invention can be practiced conveniently with the wire coatingapparatus shown in the appended drawing which is adapted for coating anelectrical conductor 5 or wire that is withdrawn from a supply spool Iirotatably supported on a shaft I mounted on the apparatus.

The apparatus comprises a frame III of cast iron, which is anchored toa. floor or other base (not shown). Secured to the bottom portion ofthis frame and also supported on the floor is an open tank l2 whichcontains a supply of enamel l3 which has been thinned with a solvent.The tank also contains a plurality of enamel applicator pulleys M forconducting the wire through the enamel bath. These pulleys, which areallof the same size, are freely supported on a shaft I5 extending acrossthe open top of the enamel supply tank and the lower portion of eachpulley periphery is immersed in the liquid enamel.

Secured to the upper Dart of the frame, above the enamel tank, is avertical oven I6 which is provided with a suitable heating means, suchas gas or electricity (not shown). This oven is capable of producing asubstantially continuous 55 preferably of rectangular cross-section andcontherefrom is an elongated but relatively short auxiliary bakingchamber 20. The auxiliary chamber is formed by extensions of the ovenside walls and both chambers may be heated from the same source. Theauxiliary chamber has a wire entry opening 2| in its bottom wall and awire exit opening 22 in its top well. The auxiliary chamber is axiallyaligned with one end enamel applicator pulley (the lefthand pulley inFig. 2) and the main chamber is axially aligned with the rest of theapplicator pulleys.

Mounted on top of the oven are a series of driven capstans 23 for movingthe wire through the apparatus, one capstan being provided for andaligned with each enamel applicator pulley I4. The capstans are fixed toa shaft 24 which is journaled in a bracket 25 mounted on the oven anddriven by anysuitable means, such as an electric motor (not shown).

A take-up spool 26 for accumulating the coated wire is fixed to arotatable shaft 21 supported on the oven wall and the shaft is driven byan electric motor or other means (not shown) in the usual manner.

Supported on the outside wallof the oven immediately above the wire exitopening 22 of the auxiliary baking chamber is an open-top recep-' tacle28 through which the wire passes after it leaves the auxiliary chamber.This receptacle (Fig. 3) may be formed of sheet metal with side walls 29tapering inwardly and converging around a small opening 30 in the bottomof the receptacle for entry of the wire thereto. Supported in thereceptacle is a mass of balls or loose particles 3| of metal, or otherhard material, which partially fills the receptacle and engages the wirein its passage through the receptacle.

In the operation of the apparatus. the wire is withdrawn from the supplyspool 6, under the action of the capstans 23, and first passes aroundone of the enamel applicator pulleys (left pulley in Fig. 2) in the tankl2 which immerses the wire in the liquid enamel. As previouslyexplained, the wire as withdrawn from the supply spool may have ridges,slivers, or other projections on its surface and these irregular areas,depending upon their configuration, may accumulate very little or asubstantial amount of the liquid enamel during passage of the wirethrough the bath.

The wire with the liquid enamel thereon then enters the opening 2| inthe bottom end of the auxiliary baking chamber and passes through thischamber. Sufficient heat is applied to the wire in the auxiliary chamberto volatilize the solvent from the enamel and to advance the setting ofthe enamel to an under-baked stage wherein the enamel becomes tough andflexible but not yet brittle. This enamel condition depends primarilyupon the quantity of heat applied to the wire and this factor iscontrolled by coordinating the temperature of the chamber with thechamber length and the wire speed or,

' in general, with the time period that the wire is in the oven. Removalof the solvent from the enamel and partial curing or setting of theenamel afiects the coating on the slevers, etc. on the wire surface andwhen the wire leaves the auxiliary chamber, these surface projectionsmay extend partially or completely through the coating.

The wire with the tough enamel coating theretion thereto causing thespheres to impact the' ridges, slivers, etc., which have a relativelythin or no'enamel coating, in a suitable manner to flatten theseprojections down to the normal surface of the wire. .The impacting andwiping motion of the particles on the plastic enamel also tends to wetthe flattened areas with enamel. During this operation, the remainingportions of the wire surface are protected by their relatively thick andtough enamel coating and, because this coating is flexible and hasnot'been fully matured, it does not tend to flake or chip of! under theimpact stresses.

The size of the spheres or particles employed in this operation can bevaried somewhat, depending upon the size of the wire in process, thetypeof enamel used, and speed of the wire through the receptacle.Materials ranging in size from particles of sand to small steel shothave been used successfully and, in general, the particles should be ofhard material, substantially spherical in shape and relatively small insize. Particularly good results have been obtained with spheres having adiameter about equal to the diameter of the wire under treatment.

After the wire leaves the receptacle, or burnisher, it travels over oneof the driving capstans 23 at the top of the oven (left-hand capstan inFig. 2) and then passes through the enamel bath a second time, incontact with one of the applicator pulleys M, where it receives a secondcoating of enamel. The wire next travels upwardly through the main ovenchamber l1, entering through the opening I8, wherein the wire and enamelare heated sufllciently to completely cure the second coating and tocomplete the curing of the first coating. The wire travels at the samespeed through the auxiliary and the main baking chambers and the mainchamber can either be heated to a substantially higher temperature ormade longer than the auxiliary chamber in order to apply a greaterquantity of heat to the wire in the main chamber. It is more convenientto heat both chambers to the same temperature, actually to have themjoined together, and to make the main chamber longer than the auxiliarychamber. With certain commonly used varnish type enamels, good resultsare obtained when the two oven chambers are maintained at the sametemperature and the main chamber is about three times as long as theauxiliary chamher.

The second coating of enamel covers any areas on the wire surface thatare bare after the wire passes through the burnisher' and the resultantcoating is complete and adequate for some fields of service. However,additional insulation is required on some types of wire and any numberof additional coatings of. enamel are applied on the wire by conductingthe wire successively through the enamel bath and through the mainchamber of the baking oven the desired number of times. The abovedescribed apparatus and methods are especially adapted to the use ofvarnish type the auxiliary baking chamber. With some of the combinationenamels, the solvent can be removed completely in the auxiliary chamberand the re,- sultant solid film is sumciently flexible for theburnishing operation.

It will be apparent that other modifications and adaptations of theabove specifically described procedures are feasible, and it is to beunderstood that the invention is restricted only by the scope of theappended claims.

What is claimed is:'

1. A method of insulating wire comprising the steps of applying liquidenamel on the wire, heating the wire only sufllciently to form theenamel into a tough and flexible coating, subsequently drawing the .wirethrough a mass of small and hard particles, then applying a secondcoating of enamel on the wire, and finally again heatin the wire to formthe enamel into a hard coating.

2. A method of insulating awire conductor having an irregular surfacecomprising the steps of coating the wire with insulation, baking saidcoating only until said insulation forms into a tough film, subsequentlydrawing the wire through a mass, of hard particles to engage and flattenthe surface irregularities, applying a second coating of insulation onthe wire, and finally rebaking the coated wire to form the enamel into ahard coating.

3. A method of insulating wire having projections extending from itssurface comprising 4. A method of insulating wire having pro- Jectionson its surface comprising the steps of applying a liquid coating ofenamel on the wire, baking the coated wire only sufficiently to formthe'enamel into a flexible film, drawing the coated wire through a massof spherical particles to fiatten the projections and wet. the flattenedareas on the wire surface with flexible enamel, subsequently applying asecond coating of enamel on the wire, and finally rebaking the coatedwire until the enamel becomes hard.

5. A method of insulating wire having mjections on its surfacecomprising the steps of.

applying a coating of enamel on the wire, heating the wire sufilcientlyto form the enamel into a tough coating but not suificiently to make theenamel hard, drawing the wire with the tough enamel coating thereonthrough .a mass of particles to flatten the projections on the wiresurface, said particles being substantially spherical in shape andhaving a diameter on the order of the diameter of the wire, applyingasecondcoating of enamel on the wire, and finally rebaking the coatedwire to completely hardenthe enamel.

6. A method of insulating wire having proiections on itssurfacecompr'ising the steps of applying a coating of thermosettingenamel on the wire, heating the coatedwire sufliciently to partiallycure the enamel and form the enamel into a flexible film, drawing .thecoated wire through a mass of particles to flatten the projections onthe wire surface and wet the flattened areas with partially curedenamel, said'particles being substantially spherical in shape, andhaving a diameter on the order of the. diameter of the wire, applying asecond coating of enamel on the wire, and finally rebaking the coatedwire to fully cure the enamel and form the enamel into a hard coating.

HAL F. FRU'I'H.

